Vol 64, No 4 (2019)

A parametric study of the features of the flow field of a plane and axisymmetric overexpanded ideal gas jet in the vicinity of the nozzle edge has been conducted over the entire theoretically admissible range of determining parameters (nozzle divergence angles, exhaust Mach numbers, jet incalculabilities, and gas adiabat indicators). The exhaust parameters that correspond to the extremes of the differential characteristics of a shockwave falling (descending) from the edge and the flow field behind it have been revealed. A significant difference in the character of changes in the characteristics of the shockwave and the flow field behind it depending on the type of symmetry of the gas jet has been found and studied.

We have analyzed the propagation of pulsed pressure produced by electric discharges in a heterogeneous liquid during well drilling. The pressure dynamics has been calculated based on theoretical analysis of the nonlinear process of the electrohydraulic effect in a heterogeneous medium. As a result of analysis, the time dependences of the relative pressure and shock front coordinate have been obtained.

The results of observation of plasmoids that were formed during periodic discharge in a flow of liquid, in particular, water, in its surrounding space during discharge and in post-discharge, have been presented. The presence of long-lived luminous formations not only in the air, but also on the surface and above the surface of nearby objects has been noted. The reasons for the appearance of such objects and their properties, which have features not only of macro-, but also micro-objects, such as Dirac’s monopole, have been analyzed.

We studied the impact of ultraviolet (UV) irradiation on stress–strain characteristics, derived from uniaxial stretching measurements, and the molecular structure (photoinduced changes) of syndiotactic 1,2-polybutadien, a polymer with thermoplastic elastomer properties. Uniaxial stretching stress–strain curves are recorded for samples subjected to UV irradiation for different times and the effects UV irradiation has on the stress–strain behavior of polymers are analyzed. Long UV irradiation is found to markedly increase the hardening of polymers: Young’s modulus and yield strength increase, while the fracture strain decreases. At the same time, we observe a sharp increase in polymer molecular weight and its considerable oxidation that particularly involves surface layers. The mechanisms of cross-linking between macromolecules and their simultaneous oxidation induced by exposure to UV light are discussed along with the role these processes play in evolution of the physical mechanical properties under UV irradiation.

The structure of a Ti−(50.9 at % Ni) nanocrystalline alloy is studied by transmission electron microscopy after annealing at 300−500°C. It is found that B2-TiNi solid solution decomposition according to a heterogeneous mechanism with formation of Ti₃Ni₄ particles develops in the subgrain structure and is suppressed in nanograins. The regularities of recovery, polygonization, and recrystallization in the grain/subgrain structure of a nanocrystalline TiNi alloy are established and their interconnection with processes of dissolution and coagulation of Ti₃Ni₄ particles is identified.

We consider a linear actuator based on a flexural force element made of a material with shape memory (SM) effect generating a useful force in one direction. A mathematical model developed for such an actuator makes it possible to connect its characteristics with functional properties of the material with the SM effect. The relations derived for the developed force and shaft displacement in dimensionless form describe the behavior of the force element in the form of a rod made of any material exhibiting a SM effect.

In this study, we have considered interaction between an aluminum oxide film magnetron-sputtered on commercially pure VT1-0 titanium and a hydrogen atmosphere. The time the system was exposed to hydrogen varied from 1 to 4 h with all other parameters remaining the same. Data for the distribution of hydrogen over the depth (film thickness) and its content in the thin-film system have been obtained, and the influence of the hold time in hydrogen on the adhesion and friction coefficient of the film has been revealed. In addition, the surface conductivity and hydrogen distribution in the aluminum oxide film have been determined.

It has been established that several parameters characterizing liquation are associated with the Debye temperature of chemical elements. The correlation factors always exceed 0.9.

The temperature and amplitude dependences of internal friction in hybrid composites consisting of unidirectional carbon fibers and glass tissues in a T-107 molten epoxy matrix have been studied. From the high-frequency portion of the internal friction background with regard to its low-frequency one, the energy of formation and migration of vacancy-like defects in an amorphous matrix of glass fiber- and carbon fiber-reinforced composites has been estimated.

The electrophysical properties of semiconductor–superconductor sandwich pairs (InP–Bi/Pb 2223, 2234, 2245) are investigated, in which homophase superconductors based on bismuth cuprates with high reproducible critical temperatures of superconducting transition T_c = 107–180 K are used. The advantage of melt solar technology for obtaining superconducting materials is demonstrated. The microstructure and phase composition of strongly anisotropic superconductors with nominal composition Bi_1.7Pb_0.3Sr₂Ca_{(n– 1)}Cu_nO_y (n = 3, 4, 5) are researched. A technique of experimental determination of superconducting transition critical temperatures T_c in single-phase and homophase HTSC samples is presented. The current–voltage characteristics of InP–Bi/Pb pairs are investigated. The relationship between the electrical resistance of sandwich pairs and superconductor critical temperature T_c is established.

Conductivity inversion in thin n-InSe films under intense pulsed laser irradiation was obser. A p–n structure based on indium selenide formed between irradiated and nonirradiated regions of a thin-film sample. It was confirmed by EDAX analysis that the composition of the sample remained the same after irradiation. The conductivity inversion is attributed to a change in the dynamics of lattice defects under heating.

Deformations of the base of a free piezoceramic resonator that represents a thin disk are visualized using holographic interferometry under high-intensity electric excitation at antiresonance frequencies of radial modes. Motion of a loading point mass along the radial coordinate is used to specify identification of partial modes and the total number and energy interaction of such modes. Four topologically compatible modes form a single mode on which the pattern of Lamb modes is superimposed under certain experimental conditions, and an implicit piston mode is obtained.

Ways to reduce ion beam intensity losses in a mass spectrometric ion source, which are caused by chromatic aberration of its immersion ion-optical system, are considered. These losses are rather significant in forming a beam from ions with a large energy spread. The reduction of aberration losses is especially important when ion sources are used jointly with mass analyzers with energy focusing. It is shown that these losses can be reduced significantly by using a new type of ion-optical system of the ion source, which includes achromatic elements. A special method for calculating such elements is given. Computer simulations have shown high efficiency of such elements in the ion-optical path of ion sources of mass spectrometers.

Nanometer-thick silicon oxide films are needed for miniaturization and increase in the working rate of electronic devices. Interpretation of the initial stages of silicon oxidation is necessary for fabrication of such structures. A theoretical model of the thermal oxidation of thin silicon monolayers that takes into account an increase in the stress in the transition (oxide–substrate) layer due to oxygen accumulation therein is proposed.

X-ray computer methods of research (projection microfocus radiography and microtomography), which are used to study the problem of hidden defects of seeds and investigate its impact on sowing quality, have been considered. The description and main characteristics of technical means that were used to obtain digital two-dimensional and three-dimensional (tomographic) X-ray images of seeds have been given and the possible ways of their quantitative computer processing and analysis have been discussed. Conclusions about the abilities of the methods of projection microfocus radiography and microtomography to study the features of the internal structures of a seed that are related to the violation of its integrity have been formulated.